In the Linux kernel, the following vulnerability has been resolved: padata: Fix refcnt handling in padata_free_shell() In a high-load arm64 environment, the pcrypt_aead01 test in LTP can lead to system UAF (Use-After-Free) issues. Due to the lengthy analysis of the pcrypt_aead01 function call, I’ll describe the problem scenario using a simplified model: Suppose there’s a user of padata named user_function
that adheres to the padata requirement of calling padata_free_shell
after serial()
has been invoked, as demonstrated in the following code: c struct request { struct padata_priv padata; struct completion *done; }; void parallel(struct padata_priv *padata) { do_something(); } void serial(struct padata_priv *padata) { struct request *request = container_of(padata, struct request, padata); complete(request->done); } void user_function() { DECLARE_COMPLETION(done) padata->parallel = parallel; padata->serial = serial; padata_do_parallel(); wait_for_completion(&done); padata_free_shell(); }
In the corresponding padata.c file, there’s the following code: c static void padata_serial_worker(struct work_struct *serial_work) { ... cnt = 0; while (!list_empty(&local_list)) { ... padata->serial(padata); cnt++; } local_bh_enable(); if (refcount_sub_and_test(cnt, &pd->refcnt)) padata_free_pd(pd); }
Because of the high system load and the accumulation of unexecuted softirq at this moment, local_bh_enable()
in padata takes longer to execute than usual. Subsequently, when accessing pd->refcnt
, pd
has already been released by padata_free_shell()
, resulting in a UAF issue with pd->refcnt
. The fix is straightforward: add refcount_dec_and_test
before calling padata_free_pd
in padata_free_shell
.
OS | Version | Architecture | Package | Version | Filename |
---|---|---|---|---|---|
Debian | 12 | all | linux | < 6.1.64-1 | linux_6.1.64-1_all.deb |
Debian | 11 | all | linux | < 5.10.205-1 | linux_5.10.205-1_all.deb |
Debian | 999 | all | linux | < 6.6.8-1 | linux_6.6.8-1_all.deb |
Debian | 13 | all | linux | < 6.6.8-1 | linux_6.6.8-1_all.deb |